Black holes are common, so where are white holes?

Black holes have long captivated the imagination of scientists and the public alike, with their mysterious and powerful gravitational pull shaping the fabric of space and time. However, amidst the fascination with black holes, one question often arises: if black holes exist, where are their theoretical counterparts known as white holes? In this article, we explore the intriguing concept of white holes and the theoretical implications of their existence in the cosmos. Delving into the current understanding of these hypothetical cosmic phenomena, we navigate the complexities of black hole theory and the enigmatic nature of white holes, offering insights into the potential role they may play in unraveling the mysteries of the universe.

What are white holes?

White holes arise from solutions to Einstein's theory of general relativity devised by Karl Schwarzschild in 1916, just one year after the theory was first published. Schwarzschild was the man who wrote mathematics describing black holes in the universe as completely collapsed bodies. He had to choose, there is nothing in general relativity that determines the direction in which time flows. You can point the watch in that particular direction, and that's what gives you this image where objects fall into a black hole. This is where gravity is attractive, but you can also choose the opposite direction in which time flows and get the opposite effect. So in addition to the black hole, Schwarzschild's mathematics also gives us a white hole once you turn the way time works.

How are white holes different from black holes?

A white hole is the opposite of a black hole. In a black hole, you have a condensed gravitational field that pulls things inward, and you have a unidirectional membrane called the event horizon. When you cross this event horizon, then you are captured, and you cannot escape this black hole. You've been grabbed by gravity, and your future is destined to be at the center of a black hole, no matter what you do. Now the white hole is the opposite. So a white hole is almost like antigravity that expels material endlessly. With a white hole, you have an event horizon, where things from the inside cross the event horizon and are expelled into the universe, and you can't actually get into the white hole. So in a black hole, you can go inside, but not outward. In a white hole, you can go outside but not inward.

Is there any evidence of white holes?

The answer is no, really. I mean, there's speculation about some strange things in the universe that might have white fingerprints. There's nothing we can point to in the same way we can point to a black hole that says, "Yes, this is a white hole." Maybe it's because of the choice we make regarding the past and the future, maybe there's only one real choice regarding the direction of the future, which means we can only have black hole solutions. Some scientists suggest that the fact that the universe is asymmetrical, we see the beginning with the Big Bang, and we have an infinite future in front of us, which means that the future is written in the universe, determines a time trend in one direction which means that only a black hole solution can exist. So, although it's mathematically possible to have a white hole, the fact that our universe is asymmetric means that it can't actually be perceived.

What might astronomers look for to discover a white hole?

People think this will be a place where things are excreted with large amounts of energy. Scientists like Roger Penrose hypothesize that a white hole is like an exit for a black hole in another universe. So the material will fall into a black hole in one universe and be expelled to another universe through a white hole. So people looked for places where energy seemed to flow into the universe, but there is nothing specific there that has a signature characteristic of a white hole.

Why white holes may not exist

While general relativity describes white holes in theory, no one knows how they might actually form. A black hole surrounds a piece of space when a star collapses to a small size, but playing this video in the opposite direction makes no physical sense. An event horizon that explodes into a functional star will look like an egg that disintegrates – a violation of statistical law that demands that the universe become more chaotic over time. Even if large white holes form, it is likely that they will not stay for long. Any material released will collide with matter in orbit, and the system will collapse into a black hole. Hal Haggard, a theoretical physicist at Bard College in New York, said: "I think a long-lived white hole is highly unlikely.

Why white holes may exist

For a while, white holes seemed to share the fate of wormholes – twists mathematically permissible for time and space and likely prohibited by reality. But in recent years, some physicists have restored white holes in an attempt to save their darker siblings from an unfitting death. Ever since Stephen Hawking realized in the seventies that black holes leak energy, physicists have debated how entities can shrink and die. If the black hole evaporates, many wonder, what happens to the inner record of everything it swallowed? General relativity will not allow information to go out and quantum mechanics prohibits its deletion. "How does a black hole die? I don't know. How is a white hole born? Maybe a white hole is the death of a black hole," Rovely said. "The two questions correlate well, but you have to violate the equations of general relativity in going from one to the other." Rovilli is the founder of the theory of annular quantum gravity, an incomplete attempt to transcend general relativity by describing space itself as built of Lego-style particles. Guided by tools from this framework, he and others describe a scenario where the black hole grows to the point that it no longer obeys the common sense rules of stars and billiard balls. At the particle level, quantum randomness takes over and a black hole can turn into a white hole.